Dot matrix printers exist in a variety of forms in the prior art. One typical high-speed dot matrix printer of the impact type is described in U.S. Pat. No. 3,703,949 issued Nov. 28, 1972 to the assignee of the present invention. The printer comprises a print head mounted upon a carriage adapted to move across a paper document. The print head is provided with a plurality of vertically aligned print wires operated in a reciprocating manner by actuating solenoids. The printer is designed to sequentially print vertically aligned dot column patterns. In one typical arrangement the print head is provided with seven vertically aligned print wires. Five adjacent dot column patterns collectively define each alphabetic and numeric character within a seven row by five column dot matrix. FIG. 2 of the above mentioned U.S. Pat. No. 3,703,949 shows typical numeric and alphabetic character patterns which collectively define a seven row by five column matrix having a capability of printing up to a maximum of 35 dots to collectively form alphabetic and numeric characters, punctuation symbols and the like. A typical character height is of the order 0.10 inches.
In many applications it is desirable to provide printers capable of producing printed formats which include the capability of printing characters of single, double and triple and even n-times the size of the standard 5.times.5 character set.
The straightforward approach toward providing such a capability is to provide a register having a plurality of stages equal in number to the number of dot columns capable of being printed along one line of print with each stage having a capability of storing a plurality of bits equal in number to the standard character height of a character which is three times the size of a standard character. A character will thus be printed within a dot matrix of 21 rows by 18 columns. Thus, the register will have to have a capability of storing 126 binary bits to print the first line of a triple size character. Assuming that printing will occur on three lines of print successively, binary information of a total 378 bits (one bit for each dot position in the 18 .times. 21 matrix) must be loaded into the register to print a single character of three times the size of a standard character. For a printer having a capability of printing 132 standard size characters per line of print, it is possible to print 46 triple size characters. This would require a total of 17,288 binary bits of information to print one line of triple size characters.